In the hybrid electric motor vehicle (HEV), as disclosed in Japanese Patent Application Publication No. 2010-162996 and Japanese Patent Application Publication No. 2007-307931, in general, a high voltage supplied from a high voltage battery is lowered to about 14V by using a DC/DC converter and charged into a low voltage battery, and a power is supplied from this low voltage battery to 12V system equipments (low voltage system equipments).
Also, the DC/DC converter generates heat at a time of lowering a high voltage to a low voltage and charging it into the low voltage battery. For this reason, there is a need to cool the DC/DC converter. In order to cool the DC/DC converter, an accessory such as a fan for sending cooling air to the DC/DC converter is used.
However, when the accessory such as a fan is used for the purpose of the cooling, the DC/DC converter itself becomes large in size, and the accessory such as a fan for cooling the DC/DC converter is to be provided separately, besides accessories for cooling heat generators other than the DC/DC converter, such as a battery pack and other heat generating components, and the respective equipments are to be cooled by providing a plurality of accessories in the motor vehicle, so that the efficiency of the cooling is poor as a whole.
Also, the accessory for cooling the DC/DC converter is to be provided besides the accessories for cooling the battery pack and the other heat generating components, so that a wide space for arranging a plurality of accessories is required.
For this reason, in Japanese Patent Application Publication No. 2008-52997 and Japanese Patent Application Publication No. 2009-18785, there has been a proposition for achieving a down sizing of the DC/DC converter and an improved efficiency of the cooling, by sharing paths for cooling the battery pack and the other heat generating components and the DC/DC converter. In Japanese Patent Application Publication No. 2008-52997 and Japanese Patent Application Publication No. 2009-18785, it is possible to cool the DC/DC converter and the battery pack and the other heat generating components by one accessory for cooling, so that the efficiency of the cooling is good, and a space for respectively arranging a plurality of accessories for cooling is unnecessary, so that it is possible to realize the down sizing of the DC/DC converter itself.
As described above, in Japanese Patent Application Publication No. 2008-52997 and Japanese Patent Application Publication No. 2009-18785, it is possible to achieve the down sizing of the DC/DC converter, the improved efficiency of the cooling, and the saving of the arrangement space, by sharing the cooling paths with the battery pack and the other heat generating components for the purpose of cooling the DC/DC converter. However, there are cases where the timings for generating heat are different depending on the usage situations and the like for the DC/DC converter and the battery pack and the other heat generating components. For this reason, the timings at which the cooling of the DC/DC converter is required and the timings at which the cooling of the battery pack and the other heat generating components is required are different. In this case, the DC/DC converter is going to be cooled in order to cool the other heat generating components, even when there is no need to cool the DC/DC converter, so that the efficiency of the cooling is poor.
Also, in order to further increase the cooling effect of the DC/DC converter, if the number of fans for sending air is increased, the device including the DC/DC converter as a whole will become large in size, and it is difficult to realize the down sizing. Also, if the number of fans for sending air is increased, it will become necessary to secure a large arrangement space for arranging a plurality of fans.
Consequently, in the hybrid electric motor vehicle, when the DC/DC converter is used at a time of lowering a high voltage to a low voltage and charging it into the low voltage battery, it is difficult to cool efficiently, and there has been a need to secure a space for arranging accessories for cooling the DC/DC converter, in addition to a space for arranging the DC/DC converter.